The mechanical coolant pump is driven by an internal combustion engine for which the coolant pump generates a coolant flow. The coolant pump is provided with a pulley wheel which is driven by a drive belt. The switchable mechanical coolant pump is provided with a clutch arrangement that makes it possible to switch off the coolant pump if no active cooling of the engine is necessary, for example, right after a cold start of the engine.
The friction clutch can be a dry friction clutch which is exposed to the environment, can only be cooled by air, and increases the axial dimension of the dry part of the coolant pump. The friction clutch can alternatively be a wet friction clutch which has the disadvantage that the friction in the wet clutch environment is much lower than in a dry clutch environment. Much higher actuation power is therefore needed to engage the wet friction clutch. The wet friction clutch can, for example, be actuated by an electromagnetic arrangement which comprises an electromagnetic coil at one side and a ferromagnetic element at the other side. To provide high magnetic forces, expensive rare earth is needed for the ferromagnetic element.